1. Field of the Invention
The present invention relates to a method for preparing a strip material by joining two strips one on the other with the strips shifted each other in the lengthwise direction, and an apparatus for the same.
2. Description of the Prior Art
As a conventional apparatus for preparing a strip material, for example, there has been known one disclosed in Japanese Patent Unexamined Publication No.078736/1988. This apparatus comprises a first conveyor extending in the longitudinal direction and capable of transferring a first strip forward while supporting the first strip from the lower side, a second conveyor located directly above the first conveyor and extending in the longitudinal direction and capable of transferring a second strip forward while supporting the second strip from the lower side, and a controlling means for joining the first and second strips one on the other to form a strip material with the strips shifted each other in the lengthwise direction by a predetermined amount by controlling operations of the first and second conveyors separately or synchronously. To form a strip material by means of such an apparatus, only the second conveyor is first actuated to transfer the second strip forward, and when the forward end of the second strip is transferred to a predetermined position, the first conveyor is caused to travel by the controlling means at the same speed and in the same direction as the second conveyor. Thus, the second strip and the first strip meet together at a joining position on the first conveyor with the strips shifted each other in the lengthwise direction by a predetermined amount and they are joined at the joining position one on the other to form a strip material.
In such a conventional method or apparatus for preparing a strip material, however, the feed rates of the first and second strips are straightforwardly determined by the traveling speeds of the first and second conveyors, respectively. Accordingly, if inequality is caused between the first and second conveyors in traveling speed even in an extremely slight degree, the second strip is joined with the first strip while being tensed or contracted. As a result, excess or shortage is caused in the length of the second strip at the time of completion of the joining, leading to a problem that quality of the resulting strip material is impaired. Further, it is required, on one hand, for providing the shift to cause the first and second conveyors to travel separately, and on the other hand, for joining the strips one on the other to cause the first and second conveyors to travel simultaneously at the same speed in the same direction. Accordingly, a special control device is required for controlling the travels of the first and second conveyors, thereby causing problems of complicated constitution and diseconomy.